The present invention relates to an (E)-2-isopropyl-5-methyl-3,5-hexadienoate compound useful as a synthetic perfume or as a synthetic intermediate in organic synthesis; a method for producing the hexadienoate compound; and a method for producing (E)-2-isopropyl-5-methyl-3,5-hexadienol. The present invention also relates to a method for producing an (E)-2-isopropyl-5-methyl-3,5-hexadienyl carboxylate useful as a bioactive substance such as an insect sex pheromone and a substance related therewith. For example, the present invention relates to a method for producing (E)-2-isopropyl-5-methyl-3,5-hexadienyl acetate, which is a sex pheromone of Dysmicoccus neobrevipes (generic name: grape pineapple mealybug).
The sex pheromones of insects are biologically active substances that are commonly secreted by female individuals and have the function of attracting male individuals. A small amount of a sex pheromone shows a strong attraction activity. The sex pheromones have been widely used as means for forecasting insect emergence or for ascertaining regional spread (i.e. invasion into a specific area) of the insect pests and as means for controlling insect pests. As the means for controlling insect pests, control methods called mass trapping, lure-and-kill or attract-and-kill, lure-and-infect or attract-and-infect, and mating disruption are widely used in practice. To utilize the sex pheromones, economical production of a required amount of pheromone compounds is required for basic research and also for application.
Dysmicoccus neobrevipes (generic name: grape pineapple mealybug, and hereinafter abbreviated as “GPMB”) is widely distributed in the tropical and subtropical zones, damages various crops, and thus is an economically critical insect pest. The distribution region of GPMB has been expanded, and it becomes also important to ascertain the geographical spread. Tabata et al. have identified a sex pheromone of GPMB as (+)-(E)-2-isopropyl-5-methyl-3,5-hexadienyl acetate. Tabata et al. have further revealed that, as compared with the (±)-(E)-compound: (±)-(E)-2-isopropyl-5-methyl-3,5-hexadienyl, (±)-(Z)-2-isopropyl-5-methyl-3,5-hexadienyl acetate, which is the (±)-(Z)-compound of a corresponding geometric isomer, has lower attraction activity in attraction tests using synthetic compounds. They have also reported, by using the samples obtained through optical resolution of (±)-(E)-2-isopropyl-5-methyl-3,5-hexadienyl acetate obtained by separation of geometric isomers, that a (+)-(E)-isomer showed substantially the same attraction activity as the natural pheromone; while a (−)-(E)-isomer: (−)-(E)-2-isopropyl-5-methyl-3,5-hexadienyl acetate, which is the corresponding optical isomer (i.e. an antipode), showed about a half attraction activity of that of (+)-(E)-isomer (J. Tabata et al., J. Chem. Ecol., 41, 194 (2015)).
There is a demand for a selective production method of the sex pheromone compound of GPMB for basic biological studies and agronomic studies of the compound. There is also a strong demand for an efficient production method capable of supplying a sufficient amount of the pheromone compound for the purpose of applied and practical use.
As an example of the synthesis of the sex pheromone of GPMB, J. Tabata et al. report a four-step synthesis in J. Chem. Ecol., 41, 194 (2015) in which diethyl isopropylmalonate is used as a starting material and the final step involves Wittig reaction with an ylide reagent produced from 2-formyl-3-methylbutyl acetate and 2-methylpropenyltriphenylphosphonium bromide.
In addition, A. Kaufmann et al. report, in Helv. Chim. Acta, 29, 1133 (1946), syntheses of 2-isopropyl-5-methyl-3,5-hexadienol as the syntheses of isomers of lavandulol, which is a perfume by H. L. Simon et al.